1. Field of the Invention
The present invention relates to wafer bonding for electronic devices, for example, microwave and power electronics.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
Recent advances in GaN device technology have shown significant promise for high performance transistors. Currently, GaN based transistors have the highest output power density for high frequency electronics with over 30 W/mm at 8 GHz [1], and 8.6 W/mm at 40 GHz [2]. Furthermore, discrete AlGaN/GaN high electron mobility transistors (HEMTs), with a rated output power as high as 180 W at 2.2 GHz, have recently been offered commercially by Eudyna (Fujitsu) for applications such as cell phone base stations, suggesting that these devices are both manufacturable and commercially viable.
While the unique properties of the III-Nitride (III-N) material system make the AlGaN/GaN HEMT an ideal candidate for microwave and high power electronics, the flexibility in design and function along with the integration available in more mature technologies, such as Si and the III-Arsenide (III-As) systems, offer exciting new possibilities when combined with the capabilities of GaN.
Although epitaxial growth techniques such as metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and hydride vapor phase epitaxy (HVPE) have traditionally been utilized to fabricate the material layer structures used in semiconductor devices, these epitaxial techniques are limited to materials of similar lattice constant, crystalline structure, and coefficient of thermal expansion. Wafer bonding, which joins two materials placed in intimate contact under elevated temperature and pressure, has proven to be effective in forming a number of heterogeneous devices from lattice-mismatched materials. These devices include GaAs/InP vertical-cavity and micro disk lasers, InGaAs/Si avalanche photodiodes, InGaAsP/AlGaAs photonic crystal lasers, and AlGaAs/GaAs/GaN heterojunction bipolar transistors (HBTs) [4].
The present invention uses wafer bonding to combine the capabilities of high speed injectors such as Si, SiGe, and the III-As or III-P system, with the high power collector capabilities of the III-N system.